Finishing my shopping list...

paulskirocks
paulskirocks Solar Expert Posts: 84 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
OK, I've been really stoked just to have my 100 watt panel, allowing me to have my two-way radios, but it's time to move forward...

I have 4 230 watt panels that I plan to run in 2 strings of 2...
I have a Morningstar MPPT Tristar 45 charge controller...
I have a Trimetric 2025 meter and 500 amp shunt...
I just ordered a Morningstar 300 watt inverter for my 12 volt side, and I plan on getting one around 2000 watts for the 24 volt system...

So, my plan is to run the strings to a (fused?) disconnect between the panels and controller... Would a couple breakers make more sense, instead of a disconnect? I will need a breaker between the inverter and batteries, a breaker between the batteries and inverter, and a small load center for the AC side... So, would I size my breaker between controller and batteries based on the total PV watts? And, do I size the breaker for the inverter based on the inverter's rated watts, and what about the peak rated power?

As well, I need to figure out how I want to mount the four panels on the roof, pick up more wire and MC-4 connectors, and I still need to get batteries...

So, I want to order all my goodies, and suggestions are welcome....
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Finishing my shopping list...

    With only two parallel strings of panels no circuit protection is required: just a disconnect will be fine. But if you want to use breakers that too is fine. The main thing is that it meets whatever code is applicable where you are. That and thinking about any possible future expansion (cheaper and easier to wire for it now, rather than have to rewire later).

    You do need circuit protection between the charge controller and batteries. It should be rated for the controller's max output which is 45 Amps continuous on the MS. That's 70 Amps by NEC regs (unless I did the math wrong). Frankly a 60 Amp breaker would do. These are nice: http://www.solar-electric.com/mr60ampdccib.html Provides circuit protection and disconnect all in one.

    You do need circuit protection between the batteries and inverter too. Again, needs to be rated for the expected current. This gets a bit trickier with inverters due to the variations in low Voltage disconnect. With some 24 Volt inverters it is programmable, with others it is fixed. Dividing the max Wattage by the low Voltage gets you the max operating current. Usually the manual for the inverter gives specific recommendations for fusing. That's the best advice to follow. With a 2 kW 24 Volt inverter it's going to be around 150 Amps.

    Make sure the wiring can handle the circuit protection rating and then some. Again the manuals often have specific wiring recommendations that are hard to beat. Do not worry too much about surge ratings; they usually don't last very long and all conductors/circuit protection can take over-current for a time (this varies with how much over and how well the heat generated can be dissipated).
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  • paulskirocks
    paulskirocks Solar Expert Posts: 84 ✭✭✭✭
    #3
    Re: Finishing my shopping list...
    Cariboocoot wrote: »
    You do need circuit protection between the charge controller and batteries. It should be rated for the controller's max output which is 45 Amps continuous on the MS. That's 70 Amps by NEC regs (unless I did the math wrong). Frankly a 60 Amp breaker would do.

    Well, I'm an electrician, but I haven't picked up a copy of the NEC in a long time! Anyways, is there a specific section for solar? I guess I better break down and get a new book... Anyways, what math did you use to come up with 70 amps? I know that on the AC side, current pull cannot exceed 80% of the breaker rating...
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Finishing my shopping list...

    There are certain aspects of the NEC for solar now. Some of it is contentious.
    The NEC circuit protection formula is maximum constant current * 1.25 * 1.25 ^ nearest available size so far as I know.

    Personally I prefer "code of good practice" which doesn't have so many arbitrary rules, but alas can not be applied everywhere. Especially not where the AHJ is particularly dim on the subject of electricity. :roll:
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: Finishing my shopping list...

    wiles is worried about nitpicking us to death sometimes. myself and bb have our own particular areas of disagreement with the nec. charge controller are specialized power supplies meant to carry a wide range of dv voltages on the input to accommodate many output voltages most of which go by the most standard battery voltages. there are some that go further than this on the output voltages, but not relevant to what i'm trying to convey here. the newer supplies encountered are mppt and have a maximum output current to them. in the case of feeding such a controller too much overall power it does self limit the current being outputted making the 1.25 x 1.25 x and round upward to next commercial value for the breaker somewhat stupid. the real problem is not the output from the controller, but is the possibility of the battery shorting anywhere along those wires. this means it is needed at the batteries and not the controller and should be rated in conjunction with the wire current carrying ability and not the controller ability. of course you don't want to cut the output of the controller off by using a 50a breaker where the controller is rated for and outputting 60a.

    enough for now. minor emergency right now.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: Finishing my shopping list...

    ok, i'm back long after the minor emergency. it seems i had to rescue a cat and i kind of paid a bit of a price for it. after licking my wounds and washing myself and the clothes (including my shoes) i was wearing all is back to its supposed normal.

    anyway, i do agree for the need to bump the value of the breaker higher than the specified 45a as the cc may output slightly higher and the breaker may not be as accurate as one might think either. to even be required the 1.25x is somewhat dumb too, but doable. i personally see nothing wrong with a 50a breaker if one were to choose to employ it. heck, if you are outputting say a max of 25a from the cc then why not a 30a or 40a breaker on that 45a cc? of course it also depends on what is available too. basically you want to guard against a short occurring that would allow the battery to want to dump huge amounts of current into the wires. the cc isn't going to do this, but a battery is capable of large currents when shorted. this is obviously not needed so much at the cc as near the battery. the wires should be rated to carry the amount of current the cc can put out plus a bit more for good measure to guard against false trips.

    now a disconnect can be put at the cc too and many employ the breaker there to do such of a task. (not sure, but i think wiles requires the breaker at the cc) i use one as a disconnect at the cc and one at my batteries for protections against large battery shorts across my wires and the breaker at the cc won't trip for a short across the wires because it is after my wires leaving the short to occur between the battery and the cc breaker.

    not sure exactly when solar was first put into the nec rules, but i do know it was there in 2005. wiles also has put articles into home power magazine. btw, my pet peeve was his requirement to send a ground wire back with the pv + and pv - wires without the requirement of going straight to a ground rod outside. this endangers the structure and people within it to lightning and its emp. his answer was to "allow" another ground rod connection to another ground rod outside first, but still was required to travel back into the structure with the pv wires. the danger is still there and it would set up ground loops if the rods are near each other or tied underground as i believe they should be. many into radio are semi familiar about the subject of ground loops, but at the very least know you don't have more than one grounding point.

    enough ranting as you will read this for yourself. the posts concerning this are on this forum too.
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  • paulskirocks
    paulskirocks Solar Expert Posts: 84 ✭✭✭✭
    #7
    Re: Finishing my shopping list...

    Alright, For anyone interested, here is a rough list of what I have, what I need, and what I want... Each week, I get more money, and I get closer to getting the 920 watt system working... For now, I've been able to at least enjoy my 2-way radios off my 100 watt setup...

    What I have:

    $1100 4 230 watt panels
    $270 100 watt panel and cheap controller
    $100 12 volt battery
    $420 charge controller
    $200 TriMetric 2520 meter
    $260 MS 300 watt inverter
    $150 dc breakers
    $160 24 volt dc to 13.8 volt dc regulated 30 amp power supply

    What I really need:

    $200 mounting hardware
    $500 wire, including some lights
    $600 four 6 volt batteries
    $200 12 volt charge controller

    What I will want:

    $500 fridge stuff
    $900 Samlex 2000 watt inverter

    _______________________________________________

    $2660 spent

    $1500 left to get functioning

    $1400 left to get fridge and inverter

    _______________________________________________

    $5560 estimated total



    I might be off a bit, but it's pretty close... Patience has been a virtue, but not too difficult, considering we haven't had power there in the 47 years we've been there...
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  • newl
    newl Solar Expert Posts: 53 ✭✭✭✭
    #8
    Re: Finishing my shopping list...

    I've held onto all of my receipts for my off grid setup. I should itemize them and share one of these days..you inspire me to do so Paul. :)
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  • paulskirocks
    paulskirocks Solar Expert Posts: 84 ✭✭✭✭
    #9
    Re: Finishing my shopping list...

    Hmm, I need a 3 amp/120 volt inline fuse and fuse holder for the output of the 300 watt inverter... Suggestions?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Finishing my shopping list...
    paulskirocks wrote: »
    Hmm, I need a 3 amp/120 volt inline fuse and fuse holder for the output of the 300 watt inverter... Suggestions?

    Yes; don't worry about it too much. The inverter will fault and shut down from overload before the fuse blows.
    Otherwise it isn't difficult to find these in the glass tube type fuses/holders. You still have Radio Shack down there? (They closed in Canada years ago.)
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